Heat From Waste
What if your shower could help heat a building?
Energy under our feet
Every day, warm water goes down sinks, showers and toilets. That heat doesn’t just disappear. It flows through the sewers beneath our cities. Most of the time, it’s wasted. But it doesn’t have to be.
Turning sewage into heat
Borders College in Scotland is using sewer water to heat its buildings. Around 95% of its heating comes from nearby wastewater. That’s heat that would normally be lost.
Some experts estimate that around 30% of the world’s energy ends up in sewers.
How does it work?
Wastewater from homes and buildings still contains warmth.
Here’s what happens:
- Liquid waste is separated from solids.
- The liquid passes through a heat exchanger.
- Heat is transferred into a clean water system (the sewage never mixes).
- A heat pump boosts the temperature.
- The heated water warms buildings.
The cooled wastewater then continues to the treatment plant as normal.
This type of system is called heat recovery.
Why does waste heat matter?
More than half of the energy humans produce is lost as heat.
This happens in:
- Power stations
- Factories
- Data centres
- Homes
- Cars
The heat itself only contributes a small amount to global warming. But if we reused it, we would need to generate less new energy — which means less CO₂ from fossil fuels.
Other surprising sources
Waste heat can come from unexpected places:
- Crematoriums heating swimming pools
- Underground train systems warming nearby homes
Data centres heating thousands of houses.
In Denmark, one data centre can heat up to 7,000 homes.
The challenge
Heat can’t travel very far. Many places that produce lots of waste heat — like power stations or steel plants — are built far away from towns and cities. One possible solution is to use waste heat to generate electricity instead, which is much easier to transport.
The Bottom Line
Huge amounts of energy are lost as heat every day — even in our sewers. By capturing and reusing that heat, we can cut waste, lower emissions and make heating more sustainable. Sometimes the clean energy solution is already right beneath our feet.
Related ideas
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Carbon Capture
Can we stop carbon dioxide before it reaches the air?
Lunar Panels
Could moonlight one day power Earth?
Let’s shape the future together
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